1. Field of the Invention
The present application relates to measurement devices, and more particularly, to articulated arm coordinate measuring.
2. Description of the Related Art
Rectilinear measuring systems, also referred to as coordinate measuring machines (PCMM's) and articulated arm measuring machines, are used to generate geometry information. In general, these instruments capture the structural characteristics of an object for use in quality control, electronic rendering and/or duplication. One example of a conventional apparatus used for coordinate data acquisition is a portable coordinate measuring machine (PCMM), which is a portable device capable of taking highly accurate measurements within a measuring sphere of the device. Such devices often include a probe mounted on an end of an arm that includes a plurality of transfer members connected together by joints. The end of the arm opposite the probe is typically coupled to a moveable base. Typically, the joints are broken down into singular rotational degrees of freedom, each of which is measured using a dedicated rotational transducer. During a measurement, the probe of the arm is moved manually by an operator to various points in the measurement sphere. At each point, the position of each of the joints must be determined at a given instant in time. Accordingly, each transducer outputs an electrical signal that varies according to the movement of the joint in that degree of freedom. Typically, the probe also generates a signal. These position signals and the probe signal are transferred through the arm to a recorder/analyzer. The position signals are then used to determine the position of the probe within the measurement sphere. See e.g., U.S. Pat. Nos. 5,829,148 and 7,174,651.
Typically, when PCMMs are used, an operator positions his hands at various locations along the arms and joints of the PCMM to move the probe into a desired position for data acquisition. During the course of a measurement session, an operator may move his hands significantly to position and reposition the PCMM. Additionally, different operators may position their hands at different locations along the PCMM. Accordingly, it can be difficult to initially calibrate a PCMM to account for the various loads applied by different operators at different locations along the PCMM.
As mentioned above, the purpose of PCMM's is to take highly accurate measurements. Accordingly, there is a continuing need to improve the accuracy of such devices.